A geothermal heating and cooling system obtains its ability to aid in the heating or cooling of a building by exploiting the general constancy of ground temperatures. A typical geothermal heating system comprises a closed loop pipe system through which water is pumped. A portion of the pipe is disposed underground in one or more (usually several), bore holes that are drilled into the ground. As the water in the pipe travels in the pipe down and up the bore hole(s), the temperature of the ground surrounding the bore holes serves to either add heat to the water in the pipe or absorb heat from the water in the pipe, depending upon whether the water within the pipe is hotter or cooler than the surrounding ground temperature.
Since the ground surrounding the one or more bore holes remains at a generally constant temperature, the water passing through the pipe can, at least theoretically can be heated or cooled to this constant temperature regardless of the season. This enables the geothermal system to deliver water for use at the building that is generally at the same temperature on a year-round basis. The water that passes through the geothermal heating piping system can be passed through a heat exchanger, to which a blower is attached to pass the air over the heat exchanger.
Most geothermal systems are used in conjunction with a mechanical refrigeration system. One method for improving the efficiency of such a mechanical refrigeration system is to immerse the heat exchanger in a liquid medium such as water. Use of water as a heat exchange medium helps to improve the efficiency because: (1) water is a better heat exchange medium than air; and (2) water in the heat exchanger can be placed at a more appropriate temperature (cooler in summer, warmer in winter) than the corresponding air. To capitalize on these efficiencies, a geothermal heating system can be coupled to a mechanical refrigeration system to provide the more appropriate temperature and water.
In order to prevent the pollution of aquifers, most geothermal energy systems are constructed as closed-loop systems, where water is constantly re-circulated through a closed-loop. A typical prior art geothermal installation is schematically represented in FIG. 1. A building 10, such as a house, school, factory, office building or the like, includes a mechanical refrigeration system 12, to which the geothermal system 36 is coupled. The mechanical refrigeration system 12 includes an inside (first) heat exchanger 14 and an outside (second) heat exchanger 18. In a heat pump-type mechanical refrigeration system, the inside heat exchanger 14 serves as an evaporator when the system 12 is serving as an air conditioner, and as a condenser when a mechanical refrigeration system 12 is serving as a heating unit. Conversely, the outside heat exchanger 18 serves as a condenser when the mechanical refrigeration system 12 is being used as an air conditioner or cooler, and serves as an evaporator when the mechanical refrigeration system 12 is being used as a heater.
The inside heat exchanger 14 includes a coil 16 through which refrigerant flows, and a fan 22 for pulling air through the inside heat exchanger 14 cabinet, to move air past and over the coil 16, so that the air thus moved by will become cooled through its contact with the coil 16 when the mechanical refrigeration system 12 is being used as an air conditioner, and will become heated when the mechanical refrigeration system 12 is using the inside heat exchanger 14 as a condenser during a heating operation. The outside heat exchanger 18 also includes a coil that is part of the closed-loop of the mechanical refrigeration system. The inside and outside heat exchangers 16, 18 can be constructed generally similarly, except that the outside heat exchanger should be weatherized to withstand outside weather conditions.
An expansion valve 24 and a compressor 26 are provided for allowing the refrigerant to expand (expansion valve 24), and to compress the refrigerant (compressor 26). The outside heat exchanger includes a cabinet 28 that contains the coil 20. The cabinet 28 includes an inflow port 30 through which water from the geothermal heat exchange system 36 can enter the interior of the cabinet 28, and an outflow port 32 from which water of the geothermal exchange system 36 can exit the cabinet 28.
The geothermal exchange system 36 is shown as comprising a closed-loop pipe system 38, wherein water or other fluid within the geothermal system 36 is re-circulated. The geothermal exchange system includes an inflow pipe 40 that brings water into the cabinet 28 of the outside heat exchanger 18, and an outflow pipe 42 that carries water away from the cabinet 28 of the outside heat exchanger 18. A pump 44 is provided for pumping water through the closed-loop geothermal heating system.
The outflow pipe 42 includes one or more subterranean portions 46, that is (are) disposed below ground level. Although only one bore hole is shown in FIG. 1, most geothermal systems include a plurality of bore holes. The inflow pipe 40 also includes a subterranean portion 48 disposed below ground level. The subterranean portions 46, 48 of the outflow pipe 42 and inflow pipe 40 are joined at a U-shaped connector 50, so that water reaching the lower “end” of the outflow pipe 42 can flow through the connector 50 into the inflow pipe 40.
The subterranean portions 46, 48 are typically positioned within one or more bore holes 52. In a “vertical” geothermal system, the bore holes may be quite deep, and may often exceed 100 feet (30.5 m) in length, and bore holes of 1000 feet (305 m) in length are not rare. Typically, a bore hole of six to eight inches (15.3 cm to 20.3 cm) in diameter is employed, as a bore hole of that size will provide enough area for the insertion of both the subterranean portions 46, 48 of the inflow pipe 40 and outflow pipe 42.
After the bore hole 52 is dug, and the subterranean portions 46, 48 of the outflow pipe 42 and inflow pipe 40 are inserted into the bore hole 52, the area around the pipe is packed with a grouting material, that may comprise bentonite. The grouting is provided both for providing stability to the hole, and also to prevent water or fluid flowing through the inflow and outflow pipes 40, 42 from coming in contact with any water and any aquifers through which the pipes 40, 42 may pass.
The depth of the bore hole will vary based on a variety of factors, including cost. For the two-separate side-by-side pipe type system shown in FIG. 1, the installer must normally employ a bore hole having a six inch (15.3 cm) diameter or greater, in order to accommodate the pipes. At typical 2007 prices, the cost of drilling a single 100 foot (30 m), six inch (0.15 m) diameter is somewhere between about $US600.00 and $US800.00. As drilling is charged as a function of both length of the bore and diameter of the bore, it is preferable to drill the hole no deeper or wider than necessary, and one can reduce costs by finding a way to employ a smaller (diameter), short (length) hole to replace a wider (longer) hole.
The second consideration relates to heat exchange capacity. As water flowing through the subterranean portions 46, 48 of the pipe exchanges heat with the ground in which the bore hole is dug, a deeper (longer) bore hole provides a greater heat exchange capacity than a shallower (shorter) bore hole, since a longer (deeper) bore hole provides a greater residence time for water within the subterranean portions 46, 48 of a geothermal system, and provides a greater surface area of “ground” with which to exchange heat.
In this regard, the Applicant has found, that a “ton” of heating or cooling capacity is typically achieved by a bore hole of between 150 and 200 feet (46 and 61 m) with a side-by-side pipe system. By way of example, to achieve four tons of heating and cooling capacity a bore holes of between 600 and 800 fee (183 and 244 m) should be drilled.
Another factor that affects the decision of how deep or long to drill the bore hole (and hence, its associated cost) relates to the heat exchange capacity of the particular materials used in constructing the subterranean portions 46, 48 of the pipe, and the grout that is disposed in the space 52 between the pipes and the edge of the bore hole. Efficiency considerations must be balanced with environmental considerations and reliability considerations that also impact the geothermal system constructor's ability to achieve optimum heat exchange capabilities. For example, although metal pipes have a greater thermal conductivity than plastics, e.g. polybutylene piping, steel and metal pipes are not preferred for use as they have a propensity to corrode, and thereby fail over a reasonably short period of time.
Environmental concerns also factor into the technologies by which one can construct a geothermal system. For example, that many jurisdictions forbid the use of “pump and dump” geothermal systems, where the water for the geothermal system is drawn from an aquifer, run through the heat exchanger, and then deposited back into the aquifer.
In order to protect the aquifer, it is often required that the system be sealed from the “soil” of the walls of the bore hole through the use of some impervious grout material (e.g. impervious bentonite clay) that prevents water in the pipe 46, 48 from leaking into the aquifer. Unfortunately, the grout adversely impacts the heat transfer capabilities of the pipe that are usually overcome by drilling the bore hole much deeper than if the pipes 46, 48 could contact the soil directly.
One improvement to the above-mentioned dual-pipe system is a concentric pipe system invented earlier by the Applicant, James Hardin. The concentric (and typically co-axial) pipe is schematically shown in FIGS. 2 and 3 as including an outer, outflow pipe 54, that preferably has a 3″ (7.6 cm) diameter, and an inflow pipe 56. The inflow pipe 56 is disposed concentrically and interiorly of the outflow pipe 54, and typically has a one or 1.25 inch (2.54 or 3.2) cm diameter.
The concentric pipe has significant benefits over the twin-pipe system shown in FIG. 1. One benefit is that it can be placed in a smaller bore hole, such as a 4″ or 4.5″ (10 or 11.5 cm) diameter bore hole, rather than the 6″ (15.25 cm) diameter bore hole typically used for the twin-pipe system shown in FIG. 1. This use of a smaller bore hole helps to reduce drilling costs, as it costs less per foot (typically $6.00 per foot for a 4 or 4.5″ bore hole (10 or 11.5 cm) versus $8.00 per foot (0.3 m) for a 6″ (15.25 cm) bore hole at 2007 prices. Additionally, because of the configuration of the concentric pipe arrangement 54, 56, a smaller gap usually exists between the exterior wall of the outflow pipe 54, and the inner wall of the bore hole. This smaller gap reduces the amount of grout that must be placed between the concentric pipe 53 and concentric pipe 58 and the bore hole wall. Using a thinner layer of grout both helps to reduce grout costs, and permits better heat exchange between concentric pipe system 58 and the grout surrounding the bore hole.
Although the above two described configurations do perform their functions in a workman-like manner, room for improvement exists. Accordingly, it is one object of the present invention to provide an improved pipe system for use in connection with a geothermal energy system.
Another known geothermal Pipe system is the Applicant's Hardin three-chambered “Bisect” pipe system, that is shown in James Hardin Published Patent Application No. 2008/0289795 A1, published 27 Nov. 2008, that performs its job in a very workmanlike manner. The Hardin Bisect pipe includes a first chamber, a second chamber, and a central chamber. The first chamber comprises an inflow chamber, the second chamber comprises an outflow chamber, and the central chamber comprises a grouting chamber. The inflow chamber and the outflow chamber are each shaped like a half-washer, with the grouting chamber being generally circular in cross section. Grout outflow ports exist at spaced intervals. The grout outflow pipes connect the grout chamber 310, to the area adjacent to the outer wall 320 of the pipe.
One of the advantages of the Hardin bisect pipe is that it is generally believed to be more efficient, than prior pipes that it replaces, and that are discussed in more detail in the Hardin published bisect patent application that is incorporated herein by reference. However, room for improvement exists. In particular, room for improvement exists in creating an even more thermally efficient piping system, and also in creating a piping system that is better suited to manufacture through an extrusion process.
One deficiency with the bisect pipe is that it generally must be made by an injection molding process, rather than an extrusion process. Injection modling creates some additional labor requirements to assemble short length pipe segments together along with requiring the user to spend larger amounts of money on tooling, as injection modling tools are typically more expensive than extrusion tools.